This invention relates to industrial door operators, and particularly to a hydraulic control system for the door operator which provides for different speeds in opening and closing the door and provides for the engagement and disengagement of a brake that holds the door against unwanted movement.
Door operators are used to open and close doors that are mounted for swinging or sliding movement between open and closed positions, or for doors that are mounted to unroll and roll up for closing and opening door openings. The industrial doors may be used for a variety of purposes such as closing the entry ways to cold storage environments. The industrial doors are typically driven between open and close positions by a reversible motor connected to a door drive mechanism.
Hydraulic systems for door operators have been proposed. Examples of hydraulic door operators are found in U.S. Pat. No. 4,296,570 issued Oct. 27, 1981 to George C. Balbach, et. al. and assigned to the assignee of this invention. In such hydraulic systems, a reversible hydraulic pump driven by an electric motor is connected by a closed loop to a reversible hydraulic motor which in turn drives the mechanical drive for the door.
The speed of operation of the door is important. When the doors are used in a cold storage environment, they should be kept open for the shortest possible duration consistent with safety. Typically, the door will be driven open at a very rapid speed and will be closed at a second, slower speed to ensure pedestrian and vehicle clearance through the door opening before closing occurs. U.S. Pat. No. 5,410,842 issued May 2, 1995 to Joel W. Watson, and assigned to the assignee of this invention, discloses a two-speed hydraulic door operator in which the speed of closing the door is slower than that of opening the door. This is accomplished by the use of a bypass valve assembly connected between the pump and hydraulic motor and operative to bypass a portion of the fluid flow from the pump to the motor when the pump is driving the motor to close the door. The bypass flow is returned to the pump. The bypass valve is disconnected from operation by a check valve when fluid flows from the pump to the hydraulic motor in a direction to drive the motor to open the door so that full fluid flow is directed to the motor during opening. This approach allows the use of an inexpensive single speed electric motor for two-speed operations and eliminates the need for a restrictive orifice in a connection between the pump and the motor which can generate heat.
The present invention is directed to a simplified two-speed hydraulic control system that also controls the disengagement of a brake that normally holds the door against movement.